Not when he's been the senate majority leader in both situations

Doesn't matter. His statements do not modify the powers of the President, or the duties of the Senate.

Just for fun, here's another irrelevant quote:

“There’s nothing in the Constitution that says the president stops being president in his last year.”

- Ruth Bader, on whether the Senate should hold hearings and a vote on the Supreme Court nomination of Merrick Garland

I think most people agree that it should be the case that we nominate and vote on a justice regardless of the term, however for years ago Mitch set a precedent. He claimed it was because we should wait for an election, when really he was being purely obstructionist and his position now is hypocritical.

In short, it’s not the President’s fault. He should nominate someone. Mitch is the one who said the Senate should not vote. The Majority Leader does have some say over the duties of the Senate as it’s up to him to bring the vote. If it doesn’t change the duties and he was derelict of his 4 years ago then I would have hoped to see some repercussions.